The present invention relates to a fiber-composite material that can be used for a sliding member such as a ball-and-roller bearing, a plain bearing or the like used for apparatuses for producing a semiconductor, precision measuring instruments, automobiles, parts for aircrafts or the like and a brake member used as a friction member for a brake disk attached to a speed controlling apparatus used upon stopping or controlling speed of a large-sized overland transportation vehicle, for example, a large-sized automobile.
Sliding members such as ball-and-roller bearings, plain bearings and the like are used in a wide range of fields such as fields of semiconductors, ceramic industry, electronic parts, production of vehicles and the like. Particularly, nowadays, a sliding member used for plain bearings, sliders, bearing-holding instruments or the like are used at 400xc2x0 C. or higher, at which oil cannot be used as a lubricant, or a low temperature at which oil is frozen in a field of space development such as development of space shuttles and space planes and a field of energy such as nuclear energy, sunlight energy, hydrogen energy and the like, while a technical revolution proceeds rapidly. Therefore, it is necessary that the sliding member itself has a small coefficient of kinetic friction and is hardly worn away. Needless to say, such a sliding member is required to have a high strength at middle and high temperatures (200-2000xc2x0 C.), a high reliability (tenacity, shock resistance), and environmental resistance (corrosion resistance, oxidation resistance, radiation resistance). The sliding member is also required to be light enough to be moved only by a small amount of force due to the latest request for energy savings.
In these circumstances, silicon nitride and silicon carbide materials have conventionally been used as sliding materials because of their high thermal resistance and high strength. However, since these materials have a high coefficient of kinetic friction of 0.5-1.0 and are prone to cause abrasion of a corresponding material, the materials are not necessarily the best as sliding materials. Further, the materials have high densities. Therefore, driving the materials consumes high energy. Further, the materials are brittle inherently, and they are very brittle if they have a small crack. Additionally, the materials do not have sufficient strength against thermal and mechanical shocks.
As a means to overcome these defects of ceramics, there are developed a ceramic based composite material (CMC) obtained by compounding continuous ceramic fibers, and it is used as a sliding material.
This material has high strength and high tenacity even at high temperatures, and has excellent shock resistance and environmental resistance. Therefore, the material is subjected to research and development as a main super heat resistant sliding material mainly in western countries.
On the other hand, as a frictional material used in a braking apparatus installed in a large-sized overland transportation vehicle, for example, a large-sized automobile, carbon fiber in carbon (hereinafter referred to as C/C composite) is widely used at present because it has a very high coefficient of friction at high temperatures and is light in weight.
In such a large-sized overland transportation vehicle, braking by a brake has to be continued for a long period of time in accordance with a change of operation conditions, or sometimes the braking by a brake has to be repeated with high frequency. As a result, in the case of the braking apparatus using a C/C composite as a friction material, the friction material is exposed in the air at a high temperature for a long period of time. Since the friction material basically has carbon fibers combustible at a high temperature as a main component, the friction material reacts with oxygen and is worn away remarkably under such conditions. Additionally, it has been reported that a serious accident nearly occurred due to the generation of smoke. However, a substitute material has not yet been found in view of a high friction resistance at a high temperature, and the flexibility required when a member made of the material is attached to a disk brake.
There has been developed a ceramic-fiber composite produced by compounding fibers into ceramic matrices formed inside a preliminary compact (fiber preform) having a predetermined shape; said matrices having been formed by chemical vapor impregnation method (CVI method), a method of firing inorganic polymers impregnated into the preliminary compact, or filling the interia portion of the precompact with ceramic powders by means of a slip casting method, and then firing the resultant body. The precompact is produced by forming yarns each constituted by generally hundreds or thousands of ceramic long fibers having diameters of about 10 xcexcm and disposing the yarns in two- or three-dimensional directions to obtain a unidirectional sheet (UD sheet) or various kinds of cloths, or laminating the sheet or the cloths.
As examples of CMC, there are known a C/C composite having carbon matrices formed in gaps among carbon fibers disposed in two- or three-dimensional directions; a SiC fiber-reinforced Sixe2x80x94SiC composite formed by impregnating a molded body containing SiC fibers and SiC particles with Si; and the like.
However, although the C/C composite is excellent in shock resistance because of high tenacity and has light weight and high hardness, the C/C composite cannot be used at high temperatures in the presence of oxygen because it is made of carbon. Thus, the use of the C/C composite as a super heat resistant sliding material was limited. Further, since the C/C composite has relatively low hardness and low compressive force, the C/C composite has a large abrasion loss when it is used for a sliding member or a braking member.
On the other hand, although a SiC fiber reinforced Sixe2x80x94SiC composite is excellent in oxidation resistance, creep resistance, and spalling resistance, a surface of the fiber is prone to be cracked. Additionally, since a drawing effect between the matrix and fibers is small because of inferiority of a SiC fiber in lubricity with Sixe2x80x94SiC or the like, the composite is inferior to the C/C composite in tenacity, and therefore, has low shock resistance. Thus, the SiC fiber reinforced Sixe2x80x94SiC composite is not suitable for a sliding member such as bearing and slider, having a complex shape or a thin portion.
The present invention has been made in consideration of such conditions, and the object of the present invention is to provide a new light-weight fiber-composite material which has a small coefficient of kinetic friction, abrasion resistance, excellent shock resistance, corrosion resistance in a strongly oxidized environment, creep resistance, and spalling resistance. Further, even if the fiber-composite material is used as a sliding material having high hardness or a friction material for a brake for a large-sized overland transportation vehicle while maintaining the excellent shock resistance and light weight of C/C composites, the fiber-composite material is not required to be replaced with a considerable frequency like C/C composites which show severe abrasion in the presence of oxygen at high temperature.
The inventors of the present invention have made various studies to achieve the aforementioned object. As a result, they have found that the aforementioned object can be achieved by a fiber-composite material comprising: an assemblage of yarns in which yarns composing at least a bundle of carbon fibers and carbon component other than the carbon fibers are three-dimensionally combined integrally so as not to separate from each other, and matrices made of a Sixe2x80x94SiC material filled in a gap between the adjoined yarns in the assemblage of yarns; the fiber-composite material having a coefficient of kinetic friction of 0.05-0.6 and a porosity of 0.5-10%, whereby firstly the material is excellent in oxidation resistance, creep resistance and spalling resistance and can be used as a sliding material in the presence of oxygen and even in conditions in which a lubricant cannot be used because of high temperatures, and secondly even if the material is used as a friction material for a disk brake in which high temperatures are inevitably generated, while keeping excellent shock resistance and light weight, the material shows sufficient abrasion resistance in the presence of oxygen, and, as a consequence, it can be continuously used without being changed so frequently as in the case of a C/C composite. The present invention has been completed on the basis of these findings.
The present inventive fiber-composite material is basically composed of 55-75 wt % of carbon, 1-10 wt % of silicon and 10-50 wt % of silicon carbide, and has matrices comprising Sixe2x80x94SiC-based materials formed integrally among assemblages of yarns comprising carbon fibers integrally formed being combined three-dimensionally so as not to separate from each other.
If matrix layers made of a Sixe2x80x94SiC material are formed as described later in detail, the matrix layers have a thickness of preferably at least 0.01 mm, more preferably at least 0.05 mm, and furthermore preferably at least 0.1 mm.
Further, the matrix preferably has an inclined composition in which the silicon concentration becomes higher as the distance from the yarns becomes farther. The aforementioned fiber-composite material may contain at least one material selected from the group consisting of boron nitride, boron, copper, bismuth, titanium, chromium, tungsten and molybdenum. It is preferable that the present fiber-composite material preferably has a coefficient of kinetic friction of 0.05-0.6 at ambient temperature and the same coefficient even under a humid condition, and that the porosity thereof is controlled within a range of 0.5% to 10%.